Tidal-Tectonic Processes and Their Implications for the Character of Europa

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Tidal-Tectonic Processesand Their Implications
for the Character ofEuropas Icy Crust
Life on Europa

• Greenberg, Geissler, Hoppa, and Tufts
• 2002

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Evolution and State of Europa Two Linked Concepts
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Europa, what a place Life, huh? What do we have
to think about to test this idea?
Why are the cracks dirty?
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A Heat Balance Favoring Life?
qs 100 mW / m2
?

• SS heat transfer and crust thickness.
• Tidal heating qcr
• Conduction v. convection in ice
• thin ice (10 km) Tidal stresses can break it.
• thick ice (25 km Nimmo and Manga, 2002) Tidal
  stresses cannot break it.

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An ice thickness near Cilix that does not favor
Life?
Nimmo et al., 2003
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To explore effects of tidally-driven (or any)
dynamics, we need a geologic time scale

• Stratigraphy gives relative ages consistent with
  intermittent and periodic changes.
• Crater counts (and a cratering model) give an age
  (in principal!) There are not enough of them.
• Relaxation of topography around craters (with an
  ice model).

Subjove hemisphere in natural color
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StratigraphyCrosscutting Relationships
From Prockter et al. (2002)
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StratigraphyCrosscutting Lenticulae
PSRD Discoveries (http//www.psrd.hawaii.edu/)
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Craters. Not enough for statistics, but v.
interesting!
Pwyll Crater thin ice
Cilix Crater thick ice
Manannán Crater very thin ice
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We dont know time very well but the geology
permits us to certainly entertain the idea of
periodic tidal forcing acting over many length
(and time?) scales.Back to tides.
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Tidal streses and energetics basicswhat we have
to think about

• The Tidal potential on Europa a 4 body problem
  nonsynchronous orbit
• Tidal heating on Europa from dissipation (can
  only occur if egt0)
• Energy is extracted from the orbit(s), causing
  them to evolve
• Ganymede, Europa and Io are in a 124 Laplace
  resonance How is this maintained? What keeps
  Europa in a nonsynchronous orbit?

-h is fixed If e goes down (circularize orbit) a
must go up (satellite moves out)
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Europas Tides over 1 orbit Fourier Components
Total Tide
Total Tide
P
CC
C
P
Total Tide
Total Tide
P
P
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Orbital Evolution Io-Europa-Ganymede-Jupiter
system

• One Picture for the origin of Laplace Resonance
  (shown in the next movie) Its because of Io (I
  dont understand this).
• 1. Io moves outward and becomes tidally-locked
  with Jupiter. (Dissipation in Io results in a
  declining e)
• 2. Europa moves out, in turn.
• 3. Europa and Io become locked in a resonance
  and then the pair become locked with Ganymede
• Question Io is very active volcanically. This
  means Qmantle is changing on time scales of
  106-108 years. If Q goes down e goes up and a
  must go down. How stable is this resonance?

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Origin of Resonance
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Cycloidal Cracking
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Cycloidal Cracking
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Formation
Dawn - crack opens perpendicular to tidal
force, travels northeast Noon - force rotates,
crack travels west Dusk - force rotations,
crack travels southeast Night not enough
stress to shear, crack stops
Next day Repeat!
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Global Lineaments
Cadmus and Minos
Conamara region
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Thin shell, Constant D
Global Lineament Orientation
T
C
T
C

1. Astypalaea Linea
2. Thynia Linea
3. Libya Linea
4. Agenor Linea
5. Cadmus Linea
6. Minos Linea

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Strike Slip Faulting
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Tidal Walking
Splitting
Right Lateral Shear
Compression
Left Lateral Shear
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(Time-Dependent?) Ridge formation
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Ridge Formation
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Habital Niches
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Tides, water and life?